The local administration of radioactive materials may be used as a treatment for cancer, and in particular for cancers which cannot be treated surgically. The radioactive materials are incorporated into devices such as microparticles, seeds and wires which are directly implanted into the cancer.
Selective internal radiation therapy (SIRT) is a form of radiation therapy which involves injecting microspheres of radioactive material into the arteries that supply the tumour.
For example, the resin based “SIR-spheres®” (SIR-spheres® is a registered trademark of Sirtex SIR-Spheres Pty Ltd) microspheres carry the 90Y isotope and are used for SIRT. 90Y is very suitable for beta radiation therapy as tumor cells are killed within a radius of 1 to 2 mm. However, beta radiation is very poor for imaging. Bremsstrahlung imaging (which uses a photon produced by the deceleration and subsequent loss of kinetic energy when the particles produced during beta decay are deflected by other charged particles in the tissue) is not very accurate as it is not a true representation of where the isotope actually is and gives poor resolution images. Therefore, it can be difficult to ascertain whether the radiation has been successfully delivered to the target organ and to what extent.
In order to solve the problem of poor imaging, “mimic” microparticles may be administered to the patient as an investigative procedure before the administration of any therapeutic microspheres. The mimic microspheres have a similar median particle diameter but are composed of a different material to the therapeutic microspheres, and may be labeled with Tc-99m which is suitable for gamma imaging techniques. For example, heat-aggregated albumin (MAA) labeled with Tc-99m (Tc99m-MAA) may be administered to liver cancer patients as an investigative procedure before any therapeutic microspheres are administered. An image of the distribution of the mimic particles from the hepatic artery is obtained from which it can be predicted where therapeutic microspheres are likely to be distributed. If an appreciable level of Tc99m-MAA is found to leave the liver rather than remaining near the tumor, then the risk of radiation exposure to surrounding healthy organs is too large and the therapeutic microspheres are either not administered or the patient receives a reduced dose.
However, mimic particles do not always accurately predict the distribution of the therapeutic particles, which can lead to an overestimate in the number of patients deemed unsuitable for therapeutic microspheres.
Existing treatments also present the following problems.
The radioactive elements often have short half-lives, and the time elapsed between the manufacture of the radioactive material and the administration to the patient may result in significant loss of activity. This in turn leads to high costs associated with manufacture and transportation of the radioactive materials to the hospital and patient.
Incomplete retention of the radionuclide on the device can result in leaching of the radionuclide into healthy, non-cancerous tissues before reaching the target organ. It is therefore desirable to have the maximum control over the dosing of the radiation as possible, in order to deliver the radiation to the target organ in preference to healthy tissues.
The radioactive material can often only accommodate one particular radioactive element, rather than two or more radioactive elements, which can restrict the versatility of the treatment program.
It is therefore an object of the invention to provide a radiolabelled material for the treatment of cancer, which overcomes the above problems. In particular, it is desirable to develop a method by which the subsequent organ distribution of therapeutic microspheres may be more accurately predicted. Further, if therapeutic microspheres are administered, it is desirable to have a reliable method for determining the precise site of radiation exposure in the patient's body in order to determine the effectiveness of the treatment and the necessity for future treatments.